Preliminary studies on chemically-induced mouse skin tumors have shown that during tumor progression of squamous cell carcinomas (SCC), a variant poorly-differentiated neoplasm, called spindle cell carcinoma (SPCC), can arise that is characterized by enhanced invasiveness and metastatic potential. We have developed cell lines that correspond to the SCC and SPCC components of the same biphasic (SCC/SPCC) primary mouse tumor, in order to identify by differential display genes that intervene in the switch from SCC to SPCC. In particular, we focused on the absence of expression of a gene homologous to the human and rat PACE4 in the SCC cell line and its overexpression in the matched SPCC cell line. Since PACE4 is one of the several protein processing enzymes known as proprotein convertases (PCs), some of which have putative roles in activating substrates that are essential for cancer development, in this application we propose to investigate the function of PCs in tumor progression. The central hypothesis to be tested is that PACE4 and another PC, furin by activating specific targets such as matrix metalloproteinases (MMPs) enhance the invasiveness of SCC cells, thus constituting important components of the chain of events leading to an advanced malignant phenotype, culminating in the SPCC. In order to achieve this objective, we plan to: 1) investigate whether PACE4 expression is a significant feature of mouse tumors induced by protocols of chemical carcinogenesis and whether this expression is closely related to enhanced invasive/metastatic behavior and/or loss of differentiation; 2) determine whether furin participates in the process of tumor progression; 3) investigate the effect of exogenous expression of PC cDNAs on the acquisition of the invasive/metastatic phenotype of papilloma and low grade non-metastatic SCC cell lines; 4) investigate the role of PCs in the activation of MMPs in culture systems as well as in primary tumors; 5) determine the probable translational value of these findings by investigating the role of PCs in human SCCs and 6) initiate studies on the cause of PC upregulation by cloning and sequencing the PACE4 promoter region and create promoter-reporter transgenic mice to evaluate gene regulation in normal tissues and induced SCCs.